Systems Reference Library
IBM System/360 System Summary
This publication provides basic information about the IBM System/360, with the objective of helping readers to achieve a general understanding of this new data processing system and the interrelationships of its models and parts. Broad system concepts, basic and optional features, and specific input/output devices are briefly discussed.
More detailed information on processing functions is in a companion publication, IBM System/360 Principles of Operation, Form A22-6821. Further de- tails on the I/O devices described are in publications announced in the weekly publications release letter.
Form A22-6810-0 File No. S360-00
Copies of this and other IBM publications can be obtained through IBM Branch offices.
Address comments concerning the content of this publication to:
IBM Corporation, Customer Manuals, Dept. B98, P.O. Box 390, Poughkeepsie, N. Y.
©1964 by International Business Machines Corporation
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Introduction to the System Concepts ... 5
System Concepts ... . Unified Design ... . Universality ... . Compatibility ... . Programming Systems ... . Main Core Storage ... . Storage Protection ... . Shared Storage ... . Large-Capacity Storage ... . Arithmetic ... . 5 5 6 6 6 6 7 7 7 7 Instructions ... 8
Open-Ended Design. . . .. 8
Interruption System ... 8
System Accuracy and Reliability. . . . .. 8
Universal Code Capability. . . . .. 9
Channels ... 9
Channel Connector . . . .. 11
Flexibility in Speed, Storage, Features, and I/O. . . .. 11
Standard Connections for I/O Devices. . . . .. 11
Multisystem ... 12
Direct Control . . . .. 12
System Panel . . . .. 12
1401 Compatibility ... 12
System Organization ... 13
Machine Addressing ... 13
Formats ... 13
Interruption and Program Status Word ... '. . . . .. 13
Control of I/O . . . 15
I/O Equipment Pertaining to ASCII . . . 15
Input/Output Devices ... 16
Visual Output . . . .. 17
IBM 2250 Display Unit Modell, 2. . . . .. 17
IBM 1015 Inquiry Display Terminal Modell, 2 17 Manual Controls ... 20
IBM 1052 Printer-Keyboard Modell ... 20
IBM 1051 Control Unit Modell, N1 ... 20
IBM 2150 Console ... 20
Contents Tapes ... 22
IBM 2400 Series Magnetic Tape Units. . . . .. 22
IBM 7340 Hypertape Drive Model 3. . . .. 23
IBM 2816 Switching Unit Modell, 2. . . . .. 23
IBM 2671 Paper Tape Reader ... . . . .. 24
Files ... 24
IBM 1302 Disk Storage Model N1, N2 ... 24
IBM 2321 Data Cell Drive Model 1. . . .. 24
IBM 7320 Drum Storage. . . . .. 25
IBM 2311 Disk Storage Drive ... 25
IBM 2841 Storage Control Unit ... 27
IBM 2301 Drum Storage ... " ... 27
Card Input/Output ... 29
IBM 1402 Card Read Punch Model N1 ... 29
IBM 1442 Card Read Punch Model N1 ... 29
Printers ... 30
IBM 1403 Printer Model 2, 3 ... 30
IBM 1404 Printer Model 2 ... 30
IBM 2201 Printer Model 3. . . . .. 31
IBM 2821 Control Unit Mod~ll, 2, 3, 4 ... 31
IBM 1443 Printer Model N1. ... 31
IBM 1445 Printer Model N1. . . . 31
Magnetic Ink ... 33
IBM 1412 Magnetic Character Model 1 and IBM 1419 Magnetic Character Modell. . . .. 33
IBM 1418 Optical Character Reader Modell, 2, 3, and IBM 1428 Alphameric Optical Reader Modell, 2, 3 ... 33
IBM 1231 Optical Mark Page Reader Model N1 ... 34
Communications . . . .. 35
IBM 2701 Data Adapter Unit . . . .. 35
IBM 2702 Transmission Control . . . .. 38
Communications Systems ... ,... 40
IBM 1030 Data Collection System ... 40
IBM 1050 Data Communication System . . . .. 40
IBM 1060 Data Communication System ... 41
IBM 1070 Process Communication System ... 42
Audio Communications ... 42
IBM 7770 Audio Response Unit Model 3 ... 42
IBM 7772 Audio Response Unit Model 3 ... 44
For Model 30, see Figure 3.
For Model 50, see Figure 4.
For Model 60, see Figure 5 (Model 62 differs only in core storage speed).
For Model 70, see Figures 6 and 7.
IBM System/360 Model 40
IBM System/360 is an entirely new data processing system, brought into existence to provide the com- prehensive range of computing versatility required by the many modern challenges of industry and science.
The models within this system are identical in concept and compatible in programming but are matched in size, speed, and cost to the various new applications and data rate demands.
The design effort for the System/360 addressed major needs that, historically, have faced the computor cus- tomer: large high-speed storage capacities; improved facilities for communications; fixed and variable-length field capabilities; and the ability to efficiently process both commercial and scientific information.
Equally as important in the basic design philosophy was the principle that the measurement of the system would not be solely in events per microsecond, but, more importantly, in answers per dollar per month.
All these objectives, and many others as significant, have been realized in the IBM System/360.
An important aid toward the accomplishment of these design objectives was a technological change, a new dimension in data processing - solid logic tech- nology. This is the first time a commercially available
Figure 1. Second and Third Generation Components
Introduction to the System Concepts
system has been built using micro-miniaturization of components and circuits. It has four direct results:
greater reliability, higher speed, lower cost, and more compactness. See Figure 1.
Data throughput has been radically increased through new principles leading to more internal ma- chine efficiency; for example, logical concepts, such as accumulators, no longer necessarily imply a type of physical structure. The engineering design for logical requirements has broken out of traditional forms and is now strictly based on cost performance.
The System/360 is generally capable of supervising itself, with little or no manual intervention for routine tasks. This is effected by the control programs, by non- stop operation, by delegation of 110 control to data channels, by a timer, by the tamperproof storage pro- tection, and by the interruption system to be discussed.
System Concepts
Unified Design
The System/360 approach does much to organize data processing and simplify the tasks of the operator
Introduction to the System Concepts 5
and problem programmer. In the range of models (30, 40, 50, 60, 62, and 70), Model 70 has about 15 times the internal performance of Model 30 when used for commercial tasks, or approximately 50 times for scien- tific problems, with the other models performing at intermediate points. The performance points through- out this range are obtained by:
The speed of the storage;
The speed of the circuits;
The amount of information moved throughout the system at one time; and
The number of events that can take place at one time.
These differences in speed and capability for simul- taneous processing greatly affect over-all performance;
none affects the appearance of the design to the pro- grammer, nor does it affect the results of any program that does not depend on time (see "Compatibility") .
Universality
The System/360 is a truly general-purpose system de- signed to meet the needs of the commercial, scientific, communications, and control system users. It obviates the choice between a "commercial" system with its decimal arithmetic, variable-length fields, editing ca- pabilities, etc., and a "scientific" system with its high storage utilization (because of binary format), high- speed arithmetic, etc. The System/360 combines an such features.
This means that applications presently assigned to various systems can be done by a single universal sys- tem; this is true whether the application is large or small and regardless of the type - commercial, com- munications, scientific, control, or mixed.
Universality has a side benefit: once the user's sys- tems personnel have been trained in the operation of one of the System/360 models, they understand all models of the system.
Com pati bi I ity
System compatibility ensures the easy growth to a larger model, whenever the user finds that necessary, with continued utility of his programs. The facility exists at any time to use small models to back up large ones - within the limits of compatibility.
The models of the IBM System/360 are fully instruc- tion set compatible with one another. This means that any program that operates on one model will operate on any other model that has the required configuration of equipment.
Compatibility may be lost where execution of a pro- gram depends on internal timings or the relationship between internal timings and input! output speed.
6
Further details concerning compatibility are given in IBM System/360 Principles of Operation, Form A22- 6821.
Programming Systems
The System/360 was designed to operate almost en- tirely under control programs. Concepts such as multi- programming and program relocation are basic in the System/360. (For all specific discussion of program- ming systems, refer to IBM System/360 Programming Systems Summary, Form C28-6510.)
Main Core Storage
Capacity of main core storage varies from 8,l92 to 524,288 bytes, depending on the system model (Figure 2). A byte consists of eight bits plus a parity (check) bit, and is the smallest addressable unit in the IBM
System/360. Storage capacities are always given in bytes.
,....~:::...-
_ _ _ _ _ _ _ -:'P_R_O_C_ES:-S_IN_G_U_N_IT _ _ _- - r / /
Main Storage f Capacity
(bytes) System Mode I 8,192 C30
16,384 D30 D40 32,768 E30 E40
65-;536- 1=30 -F40 - FSO - - - -
131,072 G40 G50 G60
262, i44- - - -H40 -H50- H60- H62- H70 524,288
I I
160 162 170I I I
Bytes per Access
Main STorage Speed 2 VS 2 .5)Js 2)Js 2*)Js 1)Js
Channels
to I/O ~
f Main Storage in Models 60-70 is housed externally to the processing unit.
* Effective access time is less than the actual time specified, becau;e of interleaving of storage.
Figure 2. Main Storage Capacity, Cycle Time, and Bytes Per Access
The history of data processing shows that the main barrier to expanding the work that can be done on a computer has been that the amount of core storage that can be addressed by a system rapidly becomes much too small as the jobs grow bigger. The System/
360, however, has in its design the logical capability of addressing up to 16,777,216 bytes. (See "Large- Capacity Storage.") For greatest storage addressing efficiency, address arithmetic is done exclusively in binary. (See "Binary Arithmetic.")
Storage Protection
Storage protection prevents the contents of specifIed 2,048-byte blocks of storage from being altered by either errors in programs or input from 110 devices. As many as 15 different programs, each existing in any number of such storage blocks (which may be non- contiguous), can be protected at anyone time. The number of programs and blocks depends on the capac- ity of main storage.
All input operations are monitored for violations of storage protection, and the control program is alerted and takes appropriate action when any such error occurs. This protection of storage, particularly vital for applications in communications, causes no loss of per- formance.
Figure 3. IBM System/360 Model 30
Shared Storage
Presently available for Model 50, the shared storage feature permits the main storage of two Model 50's to be shared and addressed by each as a single main storage. To share storage, the feature must be in- stalled on both systems.
Large-Capacity Storage
The processing power of Models 50-70 can be ex- panded by adding large-capacity storage in blocks of either 1,048,576 or 2,097,152 bytes, to a maximum of 8,388,608 bytes. This storage is addressed contiguously with main storage. Speed of large-capacity storage is 8 microseconds. The number of bytes obtained per stor- age access, and all other features of large-capacity storage except cycle time, are the same as those of the main storage of the system.
Arithmetic
Decimal Arithmetic:
The System/360 performs decimal arithmetic on signed decimal data packed two digits (or one digit and sign) per byte. Decimal operations are performed storage- to-storage, with the lengths of the variable fIelds being
Introduction to the System Concepts 7
specified in the instruction. The maximum field size is 31 digits and sign.
Sinary Arithmetic
The System/360 has 16 general registers that can be used for binary addition, subtraction, multiplication, and division; their primary use is in computing and modifying addresses within the program. The registers are all four bytes long, though two registers are some- times coupled; for example, to preserve precision of the products and quotients in multiplication and division.
Floating-Point Arithmetic
When floating-point instructions are added to or in- cluded in the instruction set, four additional registers are provided with the system; all are eight bytes long;
all floating-point arithmetic is done in them. The floating-point operations use the 16 general registers for indexing and address arithmetic.
The floating-point, which is basically a mathematical shorthand that reduces numbers to a fraction and a characteristic (exponent), can express decimal values ranging from about 2.4 X 10-78 to about 7.2 X 1075 •
The use of floating-point greatly increases the speed and efficiency of computations.
The System/360 floating-point feature includes both short precision (four bytes) and long precision (eight bytes), for the use of either at the programmer's dis- cretion. Short precision is used to minimize execution times and maximize the number of factors in storage.
Long precision is used when maximum precision is desired; all models have both precisions and operate identically.
Instructions
Most instructions in the IBM System/360 have two data addresses; either address may be a register address or a storage address. Depending on the operation to be performed, instructions are two, four, or six bytes long.
The standard set of instructions provides the basic processing and logical instructions of the system. The addition of decimal arithmetic and editing facilities - important in commercial applications - forms the commercial set. The addition of floating-point instruc- tions to the standard set forms the scientific set. Two instructions are provided to control storage protection.
The universal instruction set, a standard facility on Models 50-70 and optional on Models 30 and 40, in- cludes the standard set, the decimal, the floating-point, and the two instructions for storage protection.
8
Open-Ended Design
One of the chief lessons of the last decade of data processing is the desirability of open-ended design.
The System/360 was designed in this way, and there- fore lends itself to taking maximum advantage of new technology, new 110 devices, etc. A simple example of open-ended design is the capability of addressing more than 16,000,000 bytes of storage, thereby antic- ipating larger storage needs; another is judicious reser- vation for many new blocks of operation codes.
Interruption System
To make maximum use of a modern data processing system, some automatic procedure must be made avail- able to alert the system to an exceptional condition, the end of an 110 operation, program errors, machine errors, etc., and send the system to the appropriate routine following the detection of such an event. The system must have, in effect, the ability to pause to answer the telephone and then to resume the inter- rupted work. This automatic procedure is called an interruption system.
Also, a main requirement for systems attempting to handle communications is the ability to be interrupted in any task in order to take on a task of higher priority.
The efficiency of any interruption system is based on the amount of time it takes to safekeep the re- minders of where it was at the time of interruption, switch to the interruptive work, and then switch back to the interrupted work. This is done in the System/360 by one of the most advanced and efficient interruption systems ever conceived, suitable for the most rigorous demands of communication systems. (For further de- tails, refer to "Interruption and Program Status Word.")
System Accuracy and Reliability
All data and instructions are monitored for invalid in- formation by parity-checking throughout the system.
Also, reliability is an inherent advantage of solid logic technology.
Programs are checked as they are executed. Because any interruptions caused by machine or program errors are at once classified by the interruption system and are treated differently, program errors cannot create machine errors; in this way, the causes of malfunctions can be and are clearly separated.
The compatible design of the System/360 makes it easy to couple together, either permanently or tempo- rarily, a special system containing redundant I/O, stor- age, and processing units; thus, the expanded system can be made capable of operating even when compo- nents fail.
Figure 4. IBM System/360 Model 50
Universal Code Capability
The use of eight information bits for each character means that the System/360 can accept most character codes now in use or planned. The system provides defined operations for processing either the extension to the widely used BCD interchange code or the recently adopted American Standard Code for Information In- terchange X3.4-1963 (ASCII).
An additional advantage of the eight bit character for alphameric data is the ability to pack two decimal digits in each byte, providing high data-packing effi- ciency in storage and on tapes and disks. Such packing is possible because decimal digits require only four in- formation bits each, and is implemented because deci- mal data occur in business records more than twice as frequently as alphameric data.
Channels
Each System/360 channel directs the How of informa- tion between main storage and those input-output de- vices the channel controls. The channel relieves the processing unit of the tasks of communicating directly with 110 and permits data processing to proceed concurrently with input-output operations. The chan- nels are of two general types: multiplexor channel and selector channels.
Multiplexor Channel
The multiplexor channel, a completely new concept in data channels, separates the operations of high-speed devices from those of lower-speed devices. Operations on the channel are in two modes: a "multiplex" mode for lower data rates, and a "burst" mode for the higher.
In the multiplex mode, the single data path of the channel can be time-shared by a large number of low- speed 110 devices operating simultaneously; the chan- nel receives and sends data to them on demand. When operating in the burst mode, however, a single 110
device captures the multiplexor channel and does not relinquish it from the time it is selected until the last byte is serviced.
Examples of low-speed devices that can operate simultaneously on the multiplexor channel are:
Printers Card Punches Card Readers Terminals
The 2702 Transmission Control can transmit messages to the System/360 from many remote 1050 terminals, for instance, all of which may be operating intermit- tently or even simultaneously, but at relatively low data rates.
Introduction to the System Concepts 9
Examples of 110 devices that operate in the burst mode are tape units and disk, drum, or data cell storage.
The multiplexor channel has the effect of subdivid- ing the data path into many subchannels (as many as 256). To the programmer, each such subchannel is a separate channel, and can be programmed as such. A different device may be started on each subchannel, and controlled by its own list of channel commands.
(Refer to "Control of 110.")
The multiplexor channel attaches up to eight 110
control units and addresses as many as 256 110 de- vices, of which the number that can run simultaneously depends on the system model. Model 30 can operate 32 simultaneously, or, with an optional feature, 96. Model 40 can operate 128 devices simultaneously. ~lodel 50 can operate 128 simultaneously, or optionally, all 256.
In the multiplex mode, data processing takes place while data are being transferred, thus increasing throughput by overlapping channel operations with processing. In the burst mode, processing is not over- lapped in Models 30 and 40 but is overlapped in Model 50. (The multiplexor channel is available only for Models 30-50.)
Selector Channels
Selector channels transmit data to or from a single 110
device at a time and are capable of handling high-speed
Figure 5. IBM System/360 Model 60 10
110 devices. Each selector channel attaches up to eight
110 control units and can address as many as 256 110
devices. One lIO device per selector channel can be transmitting data at any given time; no other liO de- vice on the channel can transmit data until all data are handled for the selected device. With two or more channels, read/write/compute is possible. All selector channels might be reading or writing, or some reading and others writing, with or without simultaneous oper- ation of the Models 30-50 multiplexor channel, while processing also takes place.
In general, 110 operations on a selector channel are overlapped with processing, and all channels can oper- ate simultaneously, provided only that the processing unit's data rate capabilities are not exceeded. Nominal data rates for the selector channels range from 250 thousand bytes to 1.3 million bytes per second, de- pending on the system model and the channel op- tions selected.
The only exception to the foregoing is a special high- speed selector channel available for Model 50, which operates in non-overlap mode.
One selector channel is required on Models 130-70;
all others are optional. The number of selector channels on a given model thus ranges from none to two for the Models 30 and 40, none to four for the Model 50 (one of the four being the high-speed channel) and one to six for the Models 60-70.
Channel Connector
Available for every channel (on Models 60-70) or just one of the channels (on Models 30-50) a channel connector provides a variety of uses that magnify the flexibility of the system. One use for the channel connector is to connect a selector channel on one system to a selector channel on another system, thereby pro- viding intersystem communication. When this is done, each system appears like 110 equipment to the other.
NOTE: More than one channel connection may be made for a particular Model 30, 40, or 50, but the additional channel connector ( s) must be physically in- stalled on the other system ( s ); only one channel con- nector can be physically installed per Models 30-50.
Flexibility in Speed, Storage, Features, and 1/0 The variations in system models, core storage capacity, optional features, and 110 configuration provide a flexi- bility that permits the system to be tailored to suit the individual user's exact requirements - with the added advantage of system growth without reprogramming.
The possible combinations of units and features, with distinctions between standard and optional features on different system models, are shown in the IBM System/
360 Configurator:
Model 30: Form A24-3232 Model 40: Form A22-6813 Model 50: Form A22-6814 Model 60, 62: Form A22-6815 Model 70: Form A22-6816
Models 40-70 (Input/Output): Form A22-6823 Models 40-70 (Data Communications): Form A22-6824 Magnetic tape units and disk storage units can be employed in various combinations as high-speed 110
and for storing vast amounts of data in tape and/or disk libraries.
Input-output also includes data communications services, magnetic character readers, visual displays, many choices in rate and type of card input and card or printer output, voice output, and the numerous other
110 capabilities described under "Input/Output Devices" in this bulletin.
Standard Connections for 1/0 Devices
The physical connection between 110 devices and the channels is called the "110 interface." All devices, regardless of their differences, can be connected to the system without adding new instructions to the proc- essing unit or new channel commands. Basic control of devices of the future will be via the interface; conse- quently, 110 interface also represents an instance of open-ended design.
Introduction to the System Concepts 11
Multisystem
Several systems, of the same or different models, may be combined into a multisystem. See Figure 6. Three levels of communication among processing units are available. The largest in capacity and slowest in speed is communication via a shared I/O device; for example, a shared disk or drum storage. Faster transmissions are obtained by the direct connection between channels afforded by the channel connector previously discussed.
Finally, storage may be shared between two Model 50 processing units.
Direct Control
Direct control provides a means of exchanging control signals between two System/360 processing units, or between a System/360 and some specialized I/O device such as an analog-digital converter. Direct control by- passes the channel.
System Panel
Operator errors are reduced by minimizing the active manual controls. The system panel containing the con- trols is attached to the processing unit and functionally divided into three sections: operator control, operator intervention, and Customer Engineering maintenance.
The operator control section is physically and function- ally identical for all models; the operator intervention
Figure 6. Typical Multisystem Model 40 with Model 70 12
section is functionally similar for all models; the CE
maintenance section for each model is unique.
Control over the system is concentrated at the system panel. The controls include stop, start, and selection of the unit for initial program loading. The operator control portion can be duplicated at a console else- where in the computer area.
1401 Compatibility
With the 1401 compatibility feature, the smallest models of the System/360 can execute 1401 instructions several times faster than the 1401 system. The com- plete 1401 instruction set is provided, with provisions also for the most generally useful 1401 feature.s. This feature is used primarily as a conversion aid from 1401 systems to System/360. Only the following I/O devices available on the 1401 can be duplicated using I/O de- vices available on the System/360:
1. 729 and 7330 Magnetic Tape Units, using 2400 series tapes with the seven-track feature.
2. 1402 Card Read Punch, using the 1402 Card Read Punch Model N1.
3. 1403 Printers, using the 1403 or 2201 Printers.
4. 1311 Disk Storage Drive, using the 231Jl Disk Storage Drive.
5. 1407 Console, using the System/360 system panel with the 1052 Printer-Keyboard.
The Processing Unit houses the facilities for address- ing storage, for arithmetic and logical processing of data, and for instructing channels to communicate with external devices.
Main Storage may be either physically integrated with the processing unit or separate from it, depending on the model. No logical differences are entailed.
Channels, likewise, may be either physically inte- grated with the processing unit or separate from it, de- pending on the model, as shown in the system con- figurators. When integrated with the processing unit, the channels share, to some extent, the processing unit circuits, resulting in cost and performance differences without differences in logical function.
The System Panel is attached to the processing unit (Figure 7).
Machine Addressing
Data in core storage are usually thought of as being physically stored in a table or block, with the positions of individual items being relative to the block origin.
The System/360 makes use of this approach.
To this end, a two-part address format is used, with each address making reference to a base (the origin) and a displacement (the item location) related to that base. The base is given in the general register tagged by the instruction; the much shorter displacement is given in the instruction itself.
U sing this approach, the System/360 can address more than 16,000,000 bytes, but without wasting stor- age by carrying a long data address in each instruction.
Furthermore, many instructions have a three-part address, in which two general registers are tagged - one for the base address and the other for an index - while the displacement is still used. Thus, the System/360 can index throughout a data area, using the displacement for local movement around a data point selected from the origin.
formats
The System/360 has the capability of accepting inputs of many varying formats. Data field lengths may be fixed at one, two, four, or eight bytes, or variable from a minimum of one byte to a maximum of 256 bytes, in increments of one byte. The length of a variable field is specified within the instruction; the length of a fixed field is implicit in the instruction's operation code.
System Organization
Editing, and arithmetic operations on decimal data, are performed using variable field lengths. Decimal numbers are also packed two per byte to conserve storage space (both main and file) and speed proc- essing. This packing of decimal information also mani- fests itself in much higher I/O data rates.
Decimal numbers may also be changed to, or appear in, a "zoned" format, as required for I/O devices trans- ferring alphameric characters at the time. In the zoned format, one byte contains one character ( whether numeric, alphabetic, or special). Decimal numbers are easily changed by single instructions, from the zoned to the packed format and vice versa.
Interruption
andProgram
Status WordThe interruption system, previously discussed under
"System Concepts," makes possible the operation of a system in a non-stop environment and greatly aids the efficient use of I/O equipment. The desire to make the interruption procedure as short and simple as possible means that the method of switching between the inter- rupted program and the program that services the interruption must be quite efficient. It operates as follows:
The complete status of the System/360 is held in eight: bytes of information. This status information, which consists of the instruction counter, condition code, storage protection key, etc., is saved when an interruption occurs, and is restored when the interrup- tion has been serviced.
As soon as the interruption occurs, all the status infor- ,p1ation, together with an identification of the cause of the interruption, is combined into a double (eight-byte)
"word" called the program status word (psw). (In the System/360, a word is one of the units of information and consists of four consecutive bytes.)
The psw is stored at a fixed location, the address of which depends on the type of interruption. The system then automatically fetches a new psw from a different fixed location, the address of which is also dependent on the type of interruption. Each class of interruption has two fixed locations in main storage: one to receive the old psw when the interruption occurs, and the other to supply the new psw that governs the servicing of that class of interruption.
After the interruption has been serviced, a single instruction uses the stored psw to reset the processing unit to the status it had before the interruption.
System Organization 13
FRONT
Processing Unit
REAR
Me i n Storage Me i n Storage Processing Unit
Figure 7. Essential Units in an IBM System/360 Model 70 14
The interruption system separates interruptions into five classes:
Program interruptions are caused by various kinds of programming errors; the exact type of error is dis- played in the old psw.
Supervisor Call interruptions are caused by the pro- gram issuing an instruction to turn over control to the supervisor (a type of master control program). The cxact reason for the call is shown in the old psw.
External interruptions are caused by either an exter- nal device requiring attention or by the timer going to zero. (The external device may be a signal from any device communicating via the direct control feature.) Machine Check interruptions are caused by the machine-checking circuits detecting a machine error.
The system is automatically switched to a diagnostic procedure.
I/O interruptions are caused by an 110 unit ending an operation or otherwise needing attention. Identifica- tions of the device and channel causing the interrup- tion are stored in the old psw; in addition, the status of the device and channel is stored in a fixed location.
Some of the program interruptions, all external in- terruptions, and all 110 interruptions can be masked
(ignored); when this is done, the external and 110
interruptions are held pending and taken at a later time (governed by the control program).
During the execution of an instruction, several inter- ruptive events may occur simultaneously. When this occurs, the competing interruptions are serviced in a fixed order of priority.
Control
of
I/OEach channel exerts direct control over all the 110
devices attached to it. However, 110 operations are initiated, halted, or tested (for masked 110 interrup- tions pending) by instructions from the control pro- gram. 110 operations are initiated by the start 110 in- struction, which selects the unit and the channel that are to be used. If they are both available, the channel takes control. Using channel command words, the channel determines what operation is to be performed
(read, write, etc.) and where the data are stored.
The channel commands may be given in a list; this is called command chaining. The ability of successive channel instructions to give a sequence of different operations to the device - such as search, read, write, and check - permits the device to be reinstructed quickly, thereby increasing its effective data rate.
The channel contains the storage required for syn- chronization with the processing unit, and refers to main storage to either obtain or place information, a character or an entire message at a time. Instruction execution in the main program is not affected, except by the time delay introduced by the claiming by the channel of operating cycles between those used for the execution of program instructions.
Tbe channel indicates the end of the 110 device operations by signaling an 110 interruption, storing the unit-and-channel address in the old psw, and the channel status in a fixed eight-byte location. If the processing unit is not interruptible for 110 interrup- tions, that interruption is kept pending in the channel;
any interruption queue in the several channels is serv- iced in a fixed order of priority.
I/O Equipment Pertaining to ASCII
The following input/output equipment will read and write the American Standard Code for Information Interchange (ASCII):
Magnetic Tape (2400 Series): The IBM 2400 mag- netic tape units are code insensitive and hence can read and write ASCII at 800 bpi with an inter-record gap of 0.6 inch.
Auxiliary storage such as disk files are also code insensitive and hence can read or write ASCII.
Paper Tape: The IBM 2671 Paper Tape Reader and 2822 Paper Tape Control Unit will read the proposed American Standard perforated tape code for Informa- tion In.terchange.
It is planned that other IBM input/output equip- ment will be made available to read or write the ASCII
standard media when these are finalized.
System Organization 15
Input/Output Devices
The following 110 devices, and/or the control units for them, can be attached to an IBM System/360.
Nearly all can be attached to any model. (For the exceptions, see the system conBgurators.)
Visual
IBM 2250 Display Unit Modell, 2
IBM 2840 Display Control
IBM 1015 Inquiry Disp]ay Terminal Modell, 2
IBM 1016 Control Unit Manual Controls
IBM 1052 Printer-Keyboard Modell
IBM 1051 Control Unit Modell, Nl
IBM 2150 Console Tape
IBM 2401 Magnetic Tape Unit Modell, 2, 3
IBM 2402 Magnetic Tape Unit Modell, 2, 3
IBM 2403 Magnetic Tape Unit and Control Modell, 2, 3
IBM 2404 Magnetic Tape Unit and Control Modell, 2, 3
IBM 2803 Tape Control
IBM 2804 Tape Control
IBM 7340 Hypertape Drive Model 3
IBM 2802 Hypertape Control
IBM 2816 Switching Unit Modell, 2
IBM 2671 Paper Tape Reader
IBM 2822 Paper Tape Reader Control Unit File
IBM 1302 Disk Storage Model Nl, N2
IBM 2321 Data Cell Drive Model 1
IBM 7320 Drum Storage
IBM 2311 Disk Storage Drive
IBM 2841 Storage Control Unit
IBM 2301 Drum Storage
IBM 2820 Drum Storage Control
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Card
IllM 1402 Card Read Punch Model N 1
IBM 1442 Card Read Punch Model N 1 Print
IBM 1403 Printer Model 2, 3
IBM 1404 Printer Model 2
IllM 2201 Printer Model 3
IllM 2821 Control Unit Modell, 2, 3, 4
IBM 1443 Printer Model Nl
IllM 1445 Printer Model Nl Magnetic Ink
IBM 1419 Magnetic Character Reader Modell
IBM 1412 Magnetic Character Reader Modell Optical
IBM 1418 Optical Character Reader Modell, 2, 3
IBM 1428 Alphameric Optical Reader Modell, 2, 3
IBM 1231 Optical Mark Page Reader Model Nl Communications
IBM 2701 Data Adapter Unit
IBM 2702 Transmission Control Communications Systems
IBM 1030 Data Collection System
IBM 1050 Data Communication System
IBM 1060 Data Communication System
IllM 1070 Process Communication System Audio Communications
IBM 7770 Audio Response Unit Model 3
IRM 7772 Audio Response Unit Model 3
Visual
OutputIBM 2250 Display Unit Modell, 2
The IBM 2250 Display Unit (Figure 8) provides the System/360 with the capability of visually displaying tables, graphs, charts, and alphameric letters and figures. Data are presented within a 12-inch by 12-inch square area on the face of a 21-inch cathode ray tube.
A typical use of the 2250 is as a system operator console. Another application is the retrieval and pre- sentation of a client's account record during a tele- phone inquiry. It is possible to update the record immediately and return the corrected data to storage.
The display area contains over 1,000,000 display points that can be addressed by X and Y coordinates.
Fifty-two lines of 74 characters each can be displayed within the 12-inch square area.
A buffered system can accept data from the proc- essing unit at up to 238 thousand bytes per second;
characters can be displayed from the buffer at up to 60,000 per second. Lines may be displayed at any angle as a series of dots. Horizontal and vertical lines may be drawn by specifying only the end points of the lines; points may be displayed as fast as 16.8 microseconds per point.
The 2250 Model 1 has a self-contained control unit and is used in applications where a single console is required. The 2250 Model 2 is used for multiple displays.
Multiple Display
The IBM 2840 Display Control provides facilities for multiple display units. The standard 2840 control contains 8,192 bytes of core storage, a character gen- erator, and controls for attaching two 2250 Model 2 Display Units. Features are available for expansion to as many as eight 2250 Model 2 Display Units on a single 2840 control. Core Storage and the character generator are time shared.
2250 Display Units may be located up to 2,000 feet away from the 2840 control unit. The 2250 Model 1 or the 2840 may be attached to either a multiplexor or selector channel.
All of the following optional features are available for the 2250 Display Unit ModelL The two marked with an asterisk (*) are not available for the 2250 Model 2 because the control unit required for multiple displays already contains these items as standard equipment.
Light Pen: A hand-held, pen-like device used by the operator to identify to the program a particular point or character on the display screen. The light pen can be used alone or in conjunction with a keyboard to rearrange, delete, highlight or edit information.
Programmed Function Keyboard: A 32-key general- purpose keyboard, the keys of which are basically un- identified; with their functions defined by application- oriented interpretation programs. Illuminated and interchangeable overlays define the key functions to the operator.
Alphanumeric Keyboard is a typewriter keyboard that permits the entry of letters, numbers, and symbols into the display unit. This keyboard also controls the screen location of a movable electronic marker that can be used for data identification. Alphameric data are first displayed on the display screen and visually checked before transmission to the computer.
Character Generator* translates a byte specifying an alphameric character into analog signals necessary to trace the character on the face of the tube; relieves the processing unit of the task of character generation.
Two character sizes are program selectable.
BufJer* provides the display unit with a choice of 4,096 or 8,192 bytes of internal storage. Buffer storage may be used to regenerate displays, thereby freeing main storage for other uses.
The following three features are available only for the 2840 control:
Additional Storage provides the 2840 control with an additional 8,192 bytes of core storage. This addition brings the storage capacity to its maximum of 16,384 bytes.
Display Multiplexor - 2 Additional - provides the 2840 with the abilHy to attach two additional 2250 Model 2 Display Units. A maximum of three such multiplexors can be added.
Display Multiplexor - 6 Additional - provides the 2840 with the ability to attach six additional 2250
~1odel 2 Display Units. Only one such multiplexor may be attached to a control unit.
IBM 1015 Inquiry Display Terminal Modell, 2 This device and its IBM 1016 Control Unit make it possible for an operator to see records in main or auxiliary storage as needed, such as upon customer demand. The information is written at a rate of up to 650 characters per second, about 40 times faster than that produced for an operator by means of a typeout.
Once written, the information is retained for as long as desired.
The viewing area has the capacity for 30 lines of 40 characters each, for a total of up to 1,200 characters at a time. Horizontal spacing is ten characters to the inch;
vertical spacing, eight lines per inch. The characters standard for display are: all 36 alphameric characters plus 23 special characters. An additional four plotting characters are available as a special feature to provide a 60 by 80 matrix for plotting, such as bar graphs and trend curves.
Input/Output Devices 17
Figure 8. IBM 2250 Display Unit
18
Figure 9. IBM 1015 Inquiry Display Terminal
The 1015 consists of two functional units: the input keyboard used to signal for the records, and the output display. (See Figure 9.) Each 1016 can control up to ten Modell inquiry display terminals. To each Model 1 can be attached as many as five Model 2's, which differ only in that Modell supplies the common power and must be turned on for attached Model 2's to operate. The five Model 2's can be attached by three separate cables, in any combination of terminals per cable.
The IBM 1016 Control Units are connected to the multiplexor or selector channels. Each inquiry display terminal can be located up to 2,500 cable-feet distant from its control unit.
Input/Output Devices 19
Manual Controls
IBM 1052 Printer-Keyboard Modell
The IBM 1052 Printer-Keyboard Model 1 (Figure 10) can be attached to the system for communication be- tween the operator and the system; e.g., such operator- to-program or program-to-operator communication as program checking, program correction, and job logging.
The keyboard and the printing are electrically and mechanically independent of each other. The keyboard can be used for system input, and the printer accepts computer output. A single keyboard depression causes an I/O interruption, and a double keyboard depression signals the end of data entry.
The 1052 prints at 14.8 characters per second. It has a replaceable printing head and a typewriter style key- board.
The 1052 may be attached to Models 40-60 via the 1052 adapter in the processing unit, which adapter provides all the necessary control signals. In Model 30, the 1052 is attached via a 1051 Control Unit (Figure 10). In Models 60-70, -the 1052 may be attached via the 2150 Console (Figure II). In Models 30-50, the device operates on the multiplexor channel in the multiplex mode.
IBM 1051 Control Unit Modell, N 1
The IBM 1051 Control Unit Modell, N1 (Figure 10) provides -the control circuitry necessary when eitber the 1052 Printer Keyboard or the additional units of a 1050 system are attached to a System/360 (lVIodel 30 only).
The maximum configuration of a 1050 system at- tached via the 1051 is one 1052, one 1053 printer, one 105,1 or 1056 reader, and one 1055, 10!57, or 1058 punch.
(The 1050 system may also be connected to the System/360 via communication devices. See "IBM 1050 Data Communication System," "IBM 2701 Data Adapter
Unit," and "IBM 2702 Transmission Control.")
The optional home component recognition feature permits any component in an attached 1050 system to be turned on and off under channel control rather than by keys at the 1052 keyboard.
IBM 2150 Console
The IBM 2150 Console provides the IBM System/360 Models 60-70 with operators' controls duplicated at a station removed from the processing unit (Figure 11).
Facilities may be provided on the console for up to three operator control panels, to control any of three systems in a multisystem, which, in this case, may
Figure 10. IBM 1052 Printer-Keyboard, 1051 Control Unit, 1443 Printer, and 1442 Card Read Punch
20
Figure 11. IBM 2150 Console, 1402 Card Read Punch, and 1403 Printer include a Model 50. The console includes an adapter for the IBM 1052 Printer-Keyboard.
The need for operator manipulation of manual con-
troIs is held to a minimum by the system design and the supervisor program. The results are fewer and less serious operator errors.
Input/Output Devices 21
Tapes
IBM 2400 Series Magnetic Tape Units
The new IBM 2400 series magnetic tape units (Figure 12) provided for the System/360 read or write nine tracks on half-inch MYLAR* standard or heavy-duty magnetic tape at a density of 800 bytes per inch. A byte contains an alphameric character or two decimal digits as packed by the computer.
The following tape units and controls are available:
IBM 2401 Magnetic Tape Unit (Single drive)
IBM 2402 Magnetic Tape Unit (Two drives)
IBM 2403 Magnetic Tape Unit and Control (Single drive and a control)
IBM 2404 Magnetic Tape Unit and Control (Single drive and a simultaneous read-write control)
Each drive is available in three models:
Model 1 (22,500 bytes per second) Model 2 (45,000 bytes per second) Model 3 (90,000 bytes per second)
Each tape control can control as many as eight tape drives. The simultaneous control attaches to two chan- nels in a manner that permits a read-type operation on one tape drive to be overlapped with a simultaneous write, write tape mark, or erase tape operation on an- other drive. Controls attach to a selector or multiplexor channel and operate in the burst mode.
"'Trademark of E. I. duPont de Nemours & Co. (Inc.)
Tape controls are also available in two stand-alone versions:
IBM 2803 Tape Control
IBM 2804 Tape Control (Simultaneous)
Any model of tape drive can be controlled by any tape control. Characferistics of the three tape drive models are shown in Figure 13.
Characteri sti c Modell Model 2 Model 3
Data Rate (kbjkd)* 22.5/45 45/90 90/180
Tape Speed (ips) 28.125 56.25 112.5
Density (bpi) 800 800 800
Nominal Inter-record Gap (inches) .6 .6 .6 Nominal Inter-record Gap Time (millisec) 21.2 10.6 5.3
Rewind Time (minutes) 3.2 2.6 1
Rewind Unload Time (minutes) 2.2 2.2 1
Tape Width (inches) .5 .5 .5
Number of Tracks 9 9 9
* kb = thousands of bytes per second.
kd = thousands of decimal digits per second.
ips = inches per second.
bpi = bytes per inch.
Figure 13. Characteristics of IBM 2400 Series Magnetic Tape Drives
Figure 12. IBM 2402 Magnetic Tape Unit and 2311 Disk Storage Drive 22
An optional sixteen-address feature enables a tape control to address as many as sixteen tape drives when used with the IBM 2816 Switching Unit(s) Modell, available for switching 4, 8, 12, or 16 tape drives to anyone of from two to four control units under pro- gram control. This feature can be used with the 2401, 2402, 2403, or 2803.
An optional seven track compatible feature enables a 2400 series tape drive and control to write or read seven-track tape, which is compatible with IBM 729 and IBM 7330 Magnetic Tape Units at 200, 556, or 800 characters per inch. As part of the seven track compatible feature, a code translator feature is in- cluded to translate the BCD interchange code to the universal System/360 code.
Seven track compatible feature installations may have an optional data conversion feature that converts three 8-bit bytes to four 6-bit characters or vice versa;
for example, for handling binary data on seven-track tape.
Error correction is a standard feature of IBM 2400 series magnetic tape units; it provides error correc- tion on a reread of a record containing one or more errors in a single track. The reread automatically cor- rects almost every single track error on the nine-track tape.
Other standard features are tape in column load, whereby tape automatically enters the tape columns after a reel is mounted and threaded and the load key is pressed, and read backward, which speeds tape sorting by eliminating certain rewind operations.
IBM 7340 Hypertape Drive Model 3
The IBM 7340 Hypertape Drive Model 3 and its IBM
2802 Hypertape Control (Figure 4) provide the IBM
System/360 with the newest high performance mag- netic tape input and output.
In the low-density mode (Figure 14), the Model 3 Hypertape drive can read tape written by Model lor 2 Hypertape, with character translation performed by the System/360 program.
High reliability is provided by Hypertape's 10-track recording; all read and write errors are detected, and, when reading, all single-bit errors and 33 of the pos- sible 45 double-bit errors are corrected automatically.
Read backward (which speeds tape sorting by elim- inating certain rewinds) and automatic threading and unthreading of tape are standard features. Tape for Hypertape drives is provided inside a cartridge that eliminates all tape contamination or damage owing to manual handling.
The IBM 2802 Hypertape Control can control up to eight 7340-3 drives. It attaches to the selector or multiplexor channel if Hypertape operation is at the
Tape Speed
Recld, Write, Read Backward Rewind
Rewind Time (approximate) Recording Density (Program- control I ed)
Low High Data Packing Data Rate
112.5 inches per second
225 inches per second (after 10 sec) 112.5 inches per sec (first 10 sec) 90 seconds
1511 bytes per inch 3022 bytes per inch
Computer can pack two decimal digits in each byte
Low 170,000 bytes per second
High 340,000 bytes per second
Nominal Inter-record Gap 0.38 inches Nominal Read/Write Access Time 3.5 mil I isceconds Tape Cartridge
Tape Width Tape Length Data Capacity
Automatic Cartridge Loader Optional Feature
Change Cartridge Cycle
1 inch 1,800 feet
As many as 128,374,560 packed decimal digits and signs
30 seconds
Figure 14. Highlights of IBM 7340 Hypertape Drive Model 3
"low" data rate of 170,000 bps, or to a selector chan- nel of appropriate data handling capacity if Hyper- tape operation is at the "high" data rate of 340,000 bps. Hypertape operation at the low or high data rate is specified by the program. An optional sixteen- address feature enables the 2802 to address as many as sixteen 7340-3 drives when used with the IBM 2816 Switching Unit(s) Model 2, which is available for switching 4, 8, 12, or 16 7340-3 drives to anyone of up to four 2802 units under program control.
IBM 2816 Switching. Unit Modell, 2
With the 16-drive control feature installed on the appropriate tape controls and the addition of two
IBM 2816 Switching Units, a maximum of 16 tape drives may be controlled in common by a maximum of four tape controls. The minimum is control of four tape drives by two tape controls; any combination be- tween the minimum and maximum is available. For more than eight drives, the second switching unit is required.
Model 1 of the switching unit is used for switching tape drives in the 2400 series. The drives in the tape- switching pool may be located in any model of 2401, 2402, or 2403. The tape controls involved may be in the IBM 2403 Magnetic Tape Unit and Control or the 2803 Tape Control.
Input/Output Devices 23
~10del 2 of the switching unit is used for switching Hypertape.
If the 16-drive control feature is not installed on a tape or Hypertape control, it can control only the first eight drives in the tape or Hypertape pool.
IBM 2671 Paper Tape Reader
The IBM 2671 Paper Tape Reader (Figure 15) photo- electrically reads strips of 5-, 6-, 7 -, or 8-channel paper tape at a rate of up to 1,000 characters per second. Internal parity error detection is provided.
Tape code translation is under program control, facili- tated by various switches on the 2671. This device is especially designed for data communications, source recording, for use in scientific data processing, and for data acquisition.
Figure 15. IBM 2671 Paper Tape Reader and 2822 Paper Tape Reader Control Unit
The paper tape reader and its IBM 2822 Paper Tape Reader Control Unit are normally attached to the System/360 through the multiplexor channel but may be attached to a selector channel.
The basic 2671 reads strips of paper tape, of any lengths that are practical for operator handling. With the optional supply feature, 10% inch rolls of paper tape can be fed, from either the center of the roll
24
or from the outside of the reel. With the optional take-up feature, the tape can be rewound on a 10%
inch reel.
After acceleration time (about 18 milliseconds), the data rate reaches 1,000 characters per second for strips.
With the optional "spooling" facilities, the data rate varies between 500 and 1,000 cycles per second, de- pending on the length of a record.
Files
IBM 1302 Disk Storage Model N 1, N2
The IBM 1302 Disk Storage (Figure 16) can record and retrieve data either at random or sequentially; the random capability permits immediate access to specific areas of information without the need to sequentially examine all the data in the £Ie. The speed of the Rccess enables the user to maintain up-to-the-second data £Ies and make frequent retrievals of the data stored.
The 1302 Model N 1 contains one disk storage module; the Model N2 contains two disk storage mod- ules. Capacity per module is 112.14 million bytes (or 224.28 million packed decimal digits and signs). Eight accesses (four modules) may be connected to the System/360 through an IBM 2841 Storage Control Unit, for on-line random access to 448.56 million bytes (or 897.12 million packed decimal digits and signs) per 2841 attached. Each module has two access mechan- isms. A special feature on the control unit permits eight more access mechanisms, with four additional modules of disk storage, to be addressed by that control unit.
The recording medium consists of thin, magnetieally- coated metal disks that spin at about 1,800 revolutions per minute. Each disk surface is divided into 500 tracks; data and control information are recorded as magnetized spots on a track. Access times are 50 milliseconds minimum, 180 milliseconds maximum, and 165 milliseconds average. The transfer rate between the 1302 and the processing unit is 156 thousand bytes per second.
IBM 2321 Data Cell Drive Model 1
The IBM 2321 Data Cell Drive (Figure 17) econom- ically extends on-line random access storage capabil- ities to a volume of data beyond that of other storage devices. Each 2321 offers 400 million bytes (or 800 million packed decimal digits and signs) of on-line data. Eight 2321's may be attached to a 2841 Storage Control Unit, for a total on-line capacity of 3.2 billion bytes or 6.4 billion packed decimal digits and signs per 2841 control unit. The data rate is 55 thousand bytes per second.
